Epidemiological studies of coccidiosis in the domesticated fowl (Gallus gallus): IV. reciprocity between the immune status of floor-reared chickens and their excretion of oocysts.

Chickens reared in floorpens for 20 weeks and naturally infected with Eimeria acervulina, E. tenella, E brunetti and E. maxima suffered outbreaks of coccidiosis, subsequently developing immunity to disease caused by each species. Thereafter, fluctuations in immunity occurred, assessed by oocyst production following challenge, which did not produce clinical signs. These fluctuations where characterized by reciprocity between immunity to each species and the excretion of oocysts of the respective species. Hence, as birds approached the solidly immune state, oocyst excretion was almost completely inhibited. Immunity then began to wane, and oocyst excretion increased once more, stimulating immunity to reach such a level that oocyst excretion was again reduced, and so on. Immunity to each species developed independently in the same birds, and protection against disease was maintained for 20 weeks. Oocysts of E.acervulina, E.tenella, E.brunetti and E.maxima were first detected in the faeces of chickens after 2, 3, 4 and 9 weeks respectively. Respective peak counts occurred at 4, 4, 12 and 9 weeks.